Vibration is a type of oscillation characterised by small, limited oscillations in a system in a near balanced state. In most aspects of engineering, because mechanical vibration affects mechanical properties, aggravates fatigue and wear, and can even cause the destruction of structures, such vibration is regarded as a negative factor which needs to be controlled.
Vibration transmitted to construction workers from the operation of various powered tools such as rammers, rock drills, demolition hammers, road breakers, hammer drills, chipping hammers or saws is an area where vibration has a significant health impact directly on the operators of the powered tools. It is known in the art that the vibration frequency range that humans perceive is from 1 to 1000 Hz, with humans most sensitive to vibration of 1-80 Hz. In particular, the most harmful vibration is in the frequency range between 6 Hz and 20 Hz. When construction workers firmly grasp the handles of powered tools for increased control and efficiency of such devices, local vibration is transmitted to the hands and arms of the user, as well throughout their body.
Local vibration can result in finger arterial contraction and reduction in grasping ability, with prolonged exposure to high levels of vibration by operating hand-held machines causing issues with normal circulation as well to nervous and musculoskeletal systems. A long period of high level vibration can serious damage to the human body, cause considerable pain and even result in permanent disability with frequency and intensity of vibration key contributing factors. This leads to a practical limit as to how long an operator can safely operate the equipment, which in turn has implications for the resources required to be allocated to specific tasks.
Vibration also affects the operation of large scale (often vehicle mounted) systems such as rock breakers. As is known by persons skilled in the art, the driving pistons of such machines are fired by nitrogen gas, hydraulic oil or a combination to strike the working tool which does the shattering, cracking or splitting of the material at the work site. Excessive vibration potentially impacts the operational life of components in such systems, and can lead to break down and decreased performance.
Typical traditional dampers have the same damping coefficient for all frequencies; with a higher damper having a smaller resonant peak; and a worse vibration amplitude at high frequencies; since the damper has very stiff and sticky for small vibration displacement. To properly provide vibration suppression; high damping is needed at the resonant frequency of the system; but a lower damping at other frequencies.
Particularly in the case of hand held machines, active damping mechanisms exist which include sensors for monitoring vibrations from a source, with some arrangement to generate an opposing force with the proper phase and amplitude sufficient to attenuate the vibration. However, most active damping mechanisms dramatically increase cost and weight and can affect overall performance of tools in which they are included.
Unfortunately, most traditional passive vibration dampening systems using traditional springs or dampers (particularly for hand held tools) do not suppress vibration as (1) the worker needs to press down to hold the machine tightly in order for high operational efficiency and (2) with more compression of traditional springs or materials, there is dramatically increasing stiffness and consequently significant reduction in the amount of vibration suppression provided.